tmt88v-print

Print PNG images to Epson TM-T88V thermal printer (80mm) via ESC/POS. Sends data directly to the device (e.g. /dev/usb/lp2), no CUPS/lp.

• Resolution: 512 dots (72mm printable width).
• 1-bit output: contrast stretch + threshold. Dithering: default none; use --dither floyd-steinberg, ordered, or atkinson for halftone.
• Chunked printing for tall images (default 400px strips); data is sent to the device in small chunks to avoid buffer overflow.

Written in TypeScript, compiles to JavaScript for npm.

Install

npm install tmt88v-print

CLI

# Print image to default device (/dev/usb/lp2)
npx tmt88v-print image.png

# Custom device
npx tmt88v-print image.png --device /dev/usb/lp0

# Save ESC/POS to file instead of printing
npx tmt88v-print image.png --output out.bin

# Chunk height (default 400)
npx tmt88v-print image.png --chunk 256

# Dithering: none (default), floyd-steinberg, ordered, atkinson
npx tmt88v-print image.png --dither floyd-steinberg
npx tmt88v-print image.png --dither ordered

# Width, fit, threshold
npx tmt88v-print image.png --width 512 --fit inside --threshold 128

If the device requires root, use the full path to node (e.g. with nvm, sudo does not see it):
sudo $(which node) $(which npx) tmt88v-print image.png
Or run from the built package: sudo $(which node) dist/cli.js image.png

API

import { imageToEscpos, printImage } from 'tmt88v-print';
import * as fs from 'fs';

// Get ESC/POS buffer (options: width, fit, dither, threshold, chunkHeight)
const buffer = await imageToEscpos('image.png', {
  chunkHeight: 400,
  dither: 'floyd-steinberg', // 'none' | 'floyd-steinberg' | 'ordered' | 'atkinson'
  threshold: 128,
});
fs.writeFileSync('/dev/usb/lp2', buffer);

// Or print directly
await printImage('image.png', { device: '/dev/usb/lp2', chunkHeight: 400, dither: 'ordered' });

Linux device

Printer is usually /dev/usb/lp0, /dev/usb/lp1, etc. Check with ls /dev/usb/lp*. Add yourself to group lp to avoid sudo: sudo usermod -aG lp $USER (then logout/login).

Why chunked writing? (no handshake)

When printing to the device, data is sent in small chunks (e.g. 1 KB) with a short delay between chunks. There is no handshake: the app only writes to /dev/usb/lp*; the Linux usblp driver does not expose a “buffer ready” signal or reliable status readback. ESC/POS defines status commands (e.g. DLE EOT), but on USB they are typically not available to the application. So we use fixed-rate throttling (same chunk size and delay every time). It is deterministic: we never send more than X bytes per Y ms, which keeps the printer buffer from overflowing (avoids EIO) while keeping the stream smooth.

Example

Print the sample image (or use your own PNG):

npm run build
node examples/print-sample.js

Uses printImage() to send examples/sample.png to the default device (/dev/usb/lp2, or set PRINTER_DEVICE).

Author

Pietro Leoni – GitHub · [email protected]

License

MIT – see LICENSE.